1. Field of the Invention
The invention pertains to a method for automatic speech direction reversal whereby a reception signal with variable damping is supplied to a loudspeaker, whereby a signal put out by a microphone with a variable damping is provided as the transmission signal, whereby reception signal and microphone signal are each continuously classified as speech signal or noise, whereby the damping or attenuation of each signal that has been classified as a speech signal is adjusted to a first damping value and the other signal is adjusted to an damping value that is greater than the first, whereby in the event that both signals are classified as speech signals the previous damping values are retained, whereby in the event that both signals are classified as noise both attenuations are adjusted to a third damping value located between the first and second damping values.
The invention further pertains to a circuit configuration for implementing the method with a controllable reception attenuator, at whose input the reception signal is present and at whose output a loudspeaker signal for driving the loudspeaker is present, a controllable transmission attenuator, at whose input the microphone signal is present and at whose output the transmission signal is present, two signal/noise detectors, to one of which the reception signal or the loudspeaker signal and to the other the microphone signal or the transmission signal is supplied, and which classify the reception signal and the transmission signal continuously as speech signal or noise, and with a control logic to control the reception attenuator and the transmission attenuator, connected to the signal/noise detectors, which in one case sets the damping of the signal path whose signal has been classified as a speech signal at a first damping value and the other signal (Tx, Rx) at a second damping value larger than the first, in the event that both signals are classified as speech signals it retains the preceding damping values, and in the event that both signals are classified as noise it sets a third damping value between the first and second damping values.
Convenience and demand for comfort in telephones has greatly increased in recent years. Automatic redialling, speed dialling, and loudspeaker address are virtually standard features. The option of speaking without the use of the handset, i.e. a speakerphone, has also become a desired function of the telephone. Besides its use in the private realm, this function finds many meaningful applications, for example, in the field of office communication, as in teleconferencing, for use in automobiles, or in any other circumstances in which the hands-free telephone operation is desireable.
The fundamental difference between a normal telephone with handset and a speakerphone consists in the mode of operation: the former works in duplex mode, wherein simultaneous transmission is effected in both directions, i.e. sending and receiving. With a speakerphone, this is only possible with a very costly and unsatisfactory method. Owing to the high degree of signal amplification in both directions, any attempt to converse in duplex mode would immediately result in a strong feedback whistling, since a closed loop is produced by the acoustic coupling between the loudspeaker and the microphone. Therefore, speakerphones can only work in simplex mode, i.e. only one of the two parties can talk while the other listens. To accomplish this, one requires a circuit which determines who is speaking and then switches through the particular channel and adequately attenuates the other one. Thus, the loop amplification is kept below unity. When the telephone parties exchange roles, the circuit must determine this immediately and switch over to the appropriate channel. The circuit then works automatically in hands-free speakerphone mode with the help of a speech direction recognition in conjunction with an electronic reversing switch.
2. Description of the Related Art
A method and a circuit configuration for automatic reversal of speech direction in telephones is known, for example, from U.S. Pat. No. 5,199,065 (corresponding European Patent 0 423 537), assigned to Siemens Aktiengesellschaft.
In that method and circuit configuration, the currently inactive channel is damped relative the active channel. This means that the person who is speaking cannot hear his telephone counterpart. In addition, it is also possible to activate a so-called idle condition in which both channels are operated at half the maximum attenuation. In the event that both participants are silent or if the speaker is drowned out by noise at the listener's location, the system slowly goes to the idle state (slow idle). In the event that the speaker and the loudspeaker have roughly the same level, on the other hand, the system goes quickly to the idle state (fast idle). A speech direction reversal is only possible if the person presently speaking stops, and the person presently listening speaks.
Thus, it is not possible to interrupt the speaker. If an error signal occurs in the receiving branch, which is wrongly classified as a speech signal, it is no longer possible to even reverse the speech direction.